Investing money enough times will make all money disappear, don't try to teach me math.
Of course mathematics is such that yes, for "the last" investor contract will not have enough money
In which countries fraud is not a crime?
fraud is intentional deception to secure unfair or unlawful gain, or to deprive a victim of a legal right. (or money)
If the participant is warned in advance, then Ponzi is not a fraud.
Ponzi it is Ponzi.
The country should in the law ban Ponzi (USA banned) or not ban (Many Asia and Africe not banned). And fraud as a crime is of course forbidden in any country.